The present invention generally relates to the detection of a chemical species and, more specifically, to a method and system for detecting and identifying the chemical species using a spectroscopy system.
One major threat to civilian, government and military installations and vehicles is the threat of explosive devices. This threat typically involves an unknown and suspicious structure, such as a package, wherein it is not known whether or not the structure includes an explosive device or harmful chemicals. Hence, nondestructive, stand-off detection of such structures and the detection of contraband high explosives would greatly increase the security of installations and vehicles.
It is well known that explosive devices emit certain chemical species, such as nitroaromatics, or leave an explosive chemical residue on the structure which can be detected to determine the presence of an explosive device. High explosives, especially nitroaromatics, have a complex photochemistry which is based on the excited triplet state of nitroaromatics.
Prior art explosive detection requires physical contact with the structure. For example, in some embodiments, the structure is placed in an instrument to detect the nitroaromatic. In other embodiments, a chemical which reacts with the explosive chemical residue is placed on the structure and then tested. Further, some embodiments use neutron capture and gamma ray detection to detect the presence of the explosive device. However, each of these embodiments requires close physical contact with the structure. Hence, prior art explosive detection is not well suited for detecting nitroaromatics or other harmful chemicals at a safe stand-off distance.
Thus, there is a need in the art for a photoacoustic spectroscopy system which can detect nitroaromatics and other chemical species, at a stand-off distance.